1. Field of the Invention
The present invention relates to a method of and an apparatus for inspecting a wiring pattern formed on a printed circuit board.
2. Description of the Background Art
With reduction in size and weight as well as increase in performance of electronic parts, the wiring pattern on a printed board circuit is also refined and highly densified. Accordingly, refinement of lines, reduction of through hole diameters etc. are required.
As to such refined lines, it is further important to inspect and manage widths, disconnection, short-circuiting etc. thereof as compared with conventional patterns.
In order to inspect and manage such a wiring pattern, the printed board is photoelectrically scanned and a pattern image obtained by binarizing the wiring pattern is employed as data, which in turn are subjected to various processes for decision of defectiveness.
Such a binarized pattern image has generally been processed by a pixel operator.
FIG. 20 shows exemplary employment of a radial operator OP having eight arms. Pixels PIX which are two-dimensionally expanded in X and Y directions have respective data obtained by binarizing a wiring pattern. A logical level "1" is provided to pixels representing the wiring pattern, while another logical level "0" is provided to pixels representing areas of a base plate on which the wiring pattern is not located.
In order to cope with refinement of lines, it is necessary to reduce the pixels PIX, i.e., to improve resolution. On the other hand, the lines may include wide parts as well as narrow parts and the number of the pixels PIX should be large in order to detect various width of the wiring lines.
As a result, it is necessary to reduce the sizes and increase the number of the pixels forming the operator OP which is applied to the image of the wiring pattern.
However, such increase of the number of the pixels forming the operator OP requires increase of the number of the pixels PIX to be two-dimensionally expanded. This leads to disadvantageous increase of the amount of hardware such as shift registers for delaying image data associated with pixels serially obtained by the photoelectric scanning. It is difficult to use a large scale integrated circuit (LSI) for obtaining such a hardware, because the number of pins of the LSI is restricted to a relatively small number and the cost is considerably increased as compared with discrete elements.